The invention relates to a method and apparatus for controlling the longitudinal dynamics (speed and acceleration) of a motor vehicle.
In conventional-longitudinal dynamics control systems in the form of so-called tempomat systems, a predefinable driving speed is adjusted by means of a speed controller which generates an actuating signal as a function of the respective control deviation, and transmits it to an actuating element in the drive train (for example, a throttle flap) in order to adjust the control deviation to zero. A more sophisticated control system is described in German patent document DE 43 38 399 A1. In order to improve maintenance of the desired speed when driving downhill, the vehicle braking power is influenced via an associated control unit.
As is known, the control characteristics of such conventional vehicle longitudinal dynamics control systems become less and less satisfactory at lower driving speeds because of the increasing significance of the non-linear behaviour of the vehicle. This is important, for example, in distance control systems having a hierarchical structure, in which a longitudinal dynamics control loop is subordinate to a distance control loop. A distance control system which is described in German patent document 195 23 111.2 (not a prior publication) remedies this problem by providing a distance controller which contains an artificial neural network that is trained using a non-linear vehicle longitudinal dynamics model which is based on a characteristic map.
Furthermore, methods and apparatus for controlling the vehicle longitudinal dynamics which use non-linear vehicle longitudinal dynamics models (in the form of so-called observer concepts) are already known. A system of this type is described in German patent document DE 36 05 117 A1. In that document, the observer is used to generate optimum controller coefficients which are used to multiply integrated control differences of the control variables longitudinal speed and engine air quantity. The latter are used to generate change contributions on the basis of which, in a following reference setpoint addition component, the actuating signals for a throttle flap and a fuel injection device are generated.
One object of the present invention is to provide a method and apparatus of the generic type mentioned above for vehicle longitudinal dynamics control, which reliably controls driving speed with satisfactory control accuracy at both high and very low desired speeds, and/or driving acceleration at both low and very high driving speeds.
This and other objects and advantages are achieved by the control method and apparatus according to the invention in which controller-internal desired speed and desired acceleration values are first ascertained from data predefined on the input side (for example by the driver, or by a higher-order distance control loop) and data about the current driving state. An actuating signal for the drive train of the vehicle is then determined from the controller-internal values using an inverse vehicle longitudinal dynamics model. The current driving state in this case contains information about at least the instantaneous driving speed, (that is, current longitudinal speed), the engine speed and/or the transmission ratio; preferably, it also contains information about the current longitudinal acceleration and the instantaneous highway slope.
The inverse vehicle longitudinal dynamics model contains models of those vehicle components which are relevant to the longitudinal dynamics, such as the engine, the (generally automatic) transmission, the rear axle and the braking system. By "inverting" the vehicle longitudinal dynamics model, input-side actuating signals for the drive train and (if appropriate) the braking system can be used to ascertain the associated instantaneous values for longitudinal speed and acceleration. Such a non-linear vehicle longitudinal dynamics model is disclosed, for example, in the abovementioned German Patent document 195 23 111.2 (not a prior publication).
In this manner, reliable control of the longitudinal speed or of the longitudinal acceleration may be realized in both the high and low driving speed ranges. When this method and apparatus are used as a subordinate part of a distance control system, the latter is simplified and improved, since the subordinate control loop comprehends the non-linear vehicle behaviour. Thus, a linear vehicle behaviour; even in the low speed range, may be assumed for the design of the higher-order distance controller.
In one embodiment of the invention the inverse vehicle longitudinal dynamics model is designed to achieve high control accuracy of the longitudinal dynamics control for a motor vehicle having an automatic transmission which has a conventional torque converter and discrete step transmission.
In another embodiment of the invention, the braking system is also included in the longitudinal dynamics control.
In other embodiments of the invention, the longitudinal dynamics control device contains, as longitudinal dynamics controller, either a speed controller or an acceleration controller having a control rule which is in each case suitably implemented in the first stage.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.